How Much Does the Earth Weigh?

Considerations

• The weight of Earth is not calculated by putting the Earth on a scale; instead, it is calculated by observing the gravitational attraction between objects. Newton discovered that every object has gravitational attraction on objects around it, which causes the other objects to move.
  Assuming the objects are spherical, such as the Earth and the sun, the equation to figure the force of gravitational attraction is:
  F = G * ((M1 * M2) / R2)
  Where:
  F = Gravitational attraction
  G = Gravitational constant equal to 6.67259 x 10^-11 m^3 kg^-1 s^-2
  M1 = Mass of object 1
  M2 = Mass of object 2
  R = Distance between the two spheres
  The gravitational constant was first referred to by Newton, in relationship to his laws dealing with gravity. The units associated with the gravitational constant are necessary to cancel out the units in the equation given above; distance cubed (given in meters above), mass squared (given in kilograms above) and time squared (given in seconds above).

Size

• In 2000, University of Washington physicists calculated the weight of Earth to be 5.972 sextillion metric tons.

Features

• The weight of Earth is calculated by using a torsion balance. A torsion balance is used to record gravitational movement in objects. The first one was used to measure the weight of Earth in the 1800s. Advances to torsion balances over the years have increased the accuracy of the calculation of the weight of Earth.

Theories/Speculation

• Due to advances in devices, such as the torsion balance, and in scientific methods, scientists believe that there is less accuracy associated with the accepted weight of Earth in the late 1990s than there was even 10 years earlier.
  Advances such as have been made by University of Washington physicists are more accurate than earlier calculations, which had Earth weighing in at 5.978 sextillion metric tons. However, those advances raise questions that further advances in scientific methods and measuring devices, such as the torsion balance, are possible and probable.

Significance

• Knowing the weight of Earth is necessary to calculate the gravitational constant. The gravitational constant is used to determine how much gravitational attraction is between two objects. The gravitational constant is one of the three most important constants in the sciences, due to their roles in other calculations. The other constants are the speed of light and Planck's constant (related to quantum physics).